Untitled

<script type="text/javascript">
    window.onload = function() {
        var fontButton = document.getElementById('changeFont');

        fontButton.addEventListener('click', function(){
            document.write('<link rel="stylesheet" type="text/css" href="/France2014/css/test.css">');
        });
    }
</script>

<body id='skin' class="skin-blue">

$('#skin').addClass('skin-red').removeClass('skin-blue');

var size = 20;
    function setFontSize(s) {
        size = s;
        $('#sidebar-menu').css('font-size', '' + size + 'px');
        $('#content').css('font-size', '' + size + 'px');
    }
    function increaseFontSize() {
        setFontSize(size + 5);
    }
    function decreaseFontSize() {
        if(size > 5)
            setFontSize(size - 5);
    }

    $('#inc').click(increaseFontSize);
    $('#dec').click(decreaseFontSize);
    setFontSize(size);

<li class="dropdown tasks-menu">
   <li>
     <a href="#" class="dropdown-toggle" data-toggle="dropdown">
       <i class="fa fa-fw fa-plus" id="inc"></i>
     </a>
   </li>
 </li>
 <li class="dropdown tasks-menu">
   <li>
     <a href="#" class="dropdown-toggle" data-toggle="dropdown">
       <i class="fa fa-fw fa-minus" id="dec"></i>
     </a>
   </li>
</li>

.menu{
color:black}

#greenTheme .menu{
color:green}